Mercury Has Ice That Won't Melt

The closest planet to the sun, Mercury can experience daytime temperatures of more than 400°C. However, there are places on the planet where the sun cannot reach. Because Mercury's rotational axis has almost no tilt, its poles don't get direct sunlight, and the craters on those poles have freezing-cold depths. Water ice was found on the inner surfaces of these craters by the Messenger spacecraft. Scientist Sean C. Solomon told the New York Times that there could be upwards of 100 billion tons of ice on Mercury, enough to "encase Washington, D.C., in a frozen block two and a half miles deep."